Method of reducing stress in metal film and metal film forming method

ABSTRACT

There is provided a method of reducing stress in a metal film that is highly stressed, the method including: processing the metal film by supplying a metal chloride gas containing a metal of the metal film and a reduction gas for reducing the metal chloride gas onto the metal film; and forming a process film on the metal film to reduce stress in the metal film.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Japanese Patent Application No.2015-108432, filed on May 28, 2015, in the Japan Patent Office, thedisclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present disclosure relates to a method of reducing stress in a metalfilm and a method of forming the metal film.

BACKGROUND

In manufacturing a large-scale integration (LSI), tungsten has beenwidely used for MOSFET gate electrodes, source-drain contacts, memorywordlines and the like. A Cu wiring has been mainly used in a multilayerwiring process. However, Cu has a poor heat resistance and is easilydiffused. As such, tungsten has been used for a portion that requires aheat resistance or a portion of which an electric property maydeteriorate due to the diffusion of Cu.

A physical vapor film formation (PVD) method has been used as a filmforming process of a tungsten film. However, it is difficult to use sucha PVD method for portion that requires a high coverage rate (stepcoverage). Because of this, a chemical vapor film formation (CVD) methodwhich provides good step coverage has been performed to form thetungsten film.

As a method of forming a tungsten film (CVD-tungsten film) using such aCVD method, a method of inducing a reaction of WF₆+3H₂→W+6HF on asemiconductor wafer as a target substrate, by using a tungstenhexafluoride (WF₆) as a raw material gas and an H₂ gas as a reductiongas, is generally used.

On the other hand, when the tungsten film is formed by the CVD methodusing the WF₆ gas, fluorine contained in WF₆ reduces a gate insulationfilm in a semiconductor device, particularly in gate electrodes, memorywordlines or the like, which deteriorates an electric property of thesemiconductor device. A method of forming a CVD-tungsten film containingno fluorine is under consideration as a way to address such a problem.

As a raw material gas used in forming the CVD-tungsten film containingno fluorine, tungsten hexachloride (WCl₆) is known. Although chlorinehas a reduction property like fluorine, reactivity of chlorine is weakerthan that of fluorine. As such, chlorine is expected to hardly affectthe electric property.

In recent years, as the semiconductor device becomes finer and finer, itis difficult to use the CVD method, which is known to provide good stepcoverage, to bury a film into a complex-shaped pattern. Thus, from theviewpoint of obtaining higher step coverage, an atomic layer filmformation (ALD) method which sequentially supplies a raw material gasand a reduction gas while performing a purge process in the course ofsequentially supplying the raw material gas and the reduction gas, isgetting a lot of attention.

In some instances, when a metal film such as a tungsten film is formedby the CVD method or the ALD method, the metal film thus formed tends tobe highly-stressed. Such a metal film causes a semiconductor wafer to bebent, which is detrimental in that a desired masking is not achieved ina subsequent process, in manufacturing the semiconductor wafer. For suchreason, there is a need for a technology for allowing a metal film suchas a tungsten film used in a semiconductor device to be stressed aslittle as possible.

SUMMARY

Some embodiments of the present disclosure provide a method of reducingstress in a metal film and a method of forming the metal film.

According to one embodiment of the present disclosure, there is provideda method of reducing stress in a metal film that is highly stressed, themethod including: processing the metal film by supplying a metalchloride gas containing a metal of the metal film and a reduction gasfor reducing the metal chloride gas onto the metal film; and forming aprocess film on the metal film to reduce stress in the metal film.

According to another embodiment of the present disclosure, there isprovided a method of forming a metal film, including: forming a metalfilm on a target substrate; processing the metal film by supplying ametal chloride gas containing a metal of the metal film and a reductiongas for reducing the metal chloride gas; and forming a process film onthe metal film to reduce stress in the metal film.

According to yet another embodiment of the present disclosure, there isprovided a method of forming a metal film, including: forming a firsttungsten film as the metal film by sequentially supplying a tungstenchloride gas and a reduction gas for reducing the tungsten chloride gasonto a target substrate; and forming a second tungsten film as a processfilm on the first tungsten film by sequentially or simultaneouslysupplying the tungsten chloride gas and the reduction gas for reducingthe tungsten chloride gas onto the target substrate with the firsttungsten film formed thereon so as to reduce stress in the firsttungsten film, wherein a flow rate of the tungsten chloride gas in theforming a first tungsten film is lower than that of the tungstenchloride gas in the forming the second tungsten film.

According to still yet another embodiment of the present disclosure,there is provided a method of forming a metal film, including: forming afirst tungsten film as the metal film by supplying a WF₆ gas and areduction gas for reducing the WF₆ gas onto a target substrate; andforming a second tungsten film by sequentially or simultaneouslysupplying a tungsten chloride gas and a reduction gas for reducing thetungsten chloride gas onto the target substrate with the first tungstenfilm formed thereon.

According to still yet another embodiment of the present disclosure,there is provided non-transitory storage medium storing a program thatoperates on a computer and controls a film forming apparatus, whereinthe program, when executed, causes the computer to control the filmforming apparatus so as to perform the aforementioned method.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the presentdisclosure, and together with the general description given above andthe detailed description of the embodiments given below, serve toexplain the principles of the present disclosure.

FIGS. 1A to 1C are views schematically illustrating a principle ofdecreasing stress in a metal film according to the present disclosure.

FIG. 2 is a sectional view showing an example of a processing apparatuswhich is used for a stress reduction process.

FIG. 3 is a view showing an example of a gas supply sequence whenforming a process film.

FIG. 4 is a view showing another example of the gas supply sequence whenforming the process film.

FIG. 5 is a cross-sectional view showing a state where a first tungstenfilm is formed, in a first embodiment of a film forming method.

FIG. 6 is a view showing a relationship between the number of cycles anda film thickness when the first tungsten film is formed, in the firstembodiment of the film forming method.

FIG. 7 is across-sectional view showing a state where a second tungstenfilm is formed on the first tungsten film, in the first embodiment ofthe film forming method.

FIG. 8 is a view showing a stress reduction effect when a stressreduction process is actually performed, in the first embodiment of thefilm forming method.

FIG. 9 is a view showing a relationship between the number of cycles inthe stress reduction process and a film stress in a tungsten filmobtained by the stress reduction process, in the first embodiment of thefilm forming method.

FIG. 10 is a view showing a stress reduction effect when the stressreduction process is performed in-situ and ex-situ by varying a filmthickness of a highly-stressed tungsten film, in the first embodiment ofthe film forming method.

FIG. 11 is a cross-sectional view showing astute where a first tungstenis formed, in a second embodiment of the film forming method.

FIG. 12 is a cross-sectional view showing astute where a second tungstenfilm is formed on the first tungsten film, in the second embodiment ofthe film forming method.

FIG. 13 is a sectional view showing an example of a film formingapparatus which can be used in forming a tungsten film in-situ, in thesecond embodiment of the film forming method.

DETAILED DESCRIPTION

Hereinafter, various embodiments of the present disclosure will bespecifically described with reference to the accompanying drawings. Inthe following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the presentdisclosure. However, it will be apparent to one of ordinary skill in theart that the present disclosure may be practiced without these specificdetails. In other instances, well-known methods, procedures, systems,and components have not been described in detail so as not tounnecessarily obscure aspects of the various embodiments.

<Principle of Stress Reduction>

A principle of stress reduction will be now described.

FIGS. 1A to 1C are views schematically illustrating a principle ofstress reduction in a metal film according to the present disclosure.

For example, when a tungsten film 202 is formed on a base film 201 suchas an SiO₂ film or a TiN film using an ALD method which sequentiallysupplies a film-forming raw material gas and a reduction gas or a CVDmethod which simultaneously supplies the film-forming raw material gasand the reduction gas, a high distortion is sometimes generated betweencrystal grains 203 as shown in FIG. 1A. Such a high distortion allows aformed tungsten film 202 to be highly-stressed. Such great stress meansenough stress to cause a problem such as bending of a semiconductorwafer. In general, stress of approximately 1,000 MPa (1 GPa) or more maybe defined as a great stress.

As shown in FIG. 1B, a process of supplying a WCl₆ gas as a raw materialgas and an H₂ gas as a reduction gas to the highly-stressed tungstenfilm 202 is performed. At this time, when the raw material gas and thereduction gas are sequentially supplied, a reaction according to thefollowing Formula (1) is induced to produce HCl:WCl₆(ad)+3H₂(g)→W(s)+6HCl  (1)

Since HCl produced by this reaction has a strong etching property, itetches the tungsten film 202 by a reaction according to the followingFormula (2):W(s)+5WCl₆(g)→6WCl_(x)  (2)

Further, such an etching action etches grain boundaries of the crystalgrains 203 of the highly-stressed tungsten film 202, which alleviates adistortion between the crystal grains 203.

At this time, as shown in FIG. 1C, by the sequential supply process, aprocess film 204 is formed in gaps defined between the crystal grains203, which are generated by the etching action, and on a surface of thetungsten film 202. As a result, a tungsten film 205 including theprocess film 204, which is entirely lowly stressed, is obtained.

As described above, through the etching action by a tungsten chloridegas such as WCl₆, it is possible to reduce stress in a highly-stressedfilm.

<Stress Reduction Process>

The stress reduction process described above is to form a film using theALD method which sequentially supplies the tungsten chloride gas and thereduction gas or the CVD method which simultaneously supplies thetungsten chloride gas and the reduction gas. Among these method, the ALDmethod which forms the film as one layer may be preferably used. TheALD-based film formation is effective to alleviate surface/film energy,which noticeably enhances the effect of the stress reduction. The CVDmethod may be utilized for the process film having a thin thickness.

An example of the tungsten chloride may include WCl₅ and WCl₄ inaddition to WCl₆. Among them, WCl₆ may be preferably used in someapplications.

Further, the reduction gas is not limited to the H₂ gas but may be otherreduction gases which contain hydrogen. Instead of the H₂ gas, an SiH₄gas, a B₂H₆ gas, an NH₃ gas or the like may be used as the reductiongas. Alternatively, two or more of the H₂ gas, the SiH₄ gas, the B₂H₆gas and the NH₃ gas may be supplied. Moreover, in addition to thesegases, other reduction gases such as a PH₃ gas or an SiH₂Cl₆ gas may beused. From the viewpoint of further decreasing impurities in the film toobtain a low resistance value, the H₂ gas may be used.

Even if the combination of the tungsten chloride gas and the reductiongas is applied, if the tungsten film is not effectively etched, it isdifficult to obtain a stress reduction effect. That is to say, thestress reduction process needs to be performed under a condition thatthe highly-stressed tungsten film can be effectively etched. On thecontrary, a tungsten film formed by the ALD method or the CVD methodusing the tungsten chloride gas and the reduction gas under a conditionthat there is no stress reduction effect, may likely become ahighly-stressed tungsten film.

An etching property in the stress reduction process depends on a flowrate of supplied tungsten chloride gas. Since an appropriate range ofthe flow rate of the tungsten chloride gas varies depending on, e.g.,the size of a chamber, a partial pressure of the tungsten chloride gasinside the chamber may be used as an indicator of the flow rate of thetungsten chloride gas. When a WCl₆ gas is used as the tungsten chloridegas, a partial pressure of the WCl₆ gas may fall within a range ofapproximately 0.5 to 10 Torr (66.7 to 1,333 Pa) from the viewpoint ofobtaining an effective etching action and inhibiting an over-etching.

In some embodiments, a temperature of the wafer in the stress reductionprocess may be 300 degrees C. or more. Further, in some embodiments, theinside of the chamber may fall within a range of 20 to 100 Torr (2,666to 13,330 Pa).

A thickness of the process film which is formed by the stress reductionprocess may be appropriately set depending on a stress value or filmthickness of the highly-stressed tungsten film. Even if the thickness ofthe process film is thin, the stress reduction effect may be obtained.In order to obtain an effective stress reduction effect, the filmthickness of the process film may fall within a range of approximately0.5 to 20 nm. By adjusting the film thickness of the process film whichis formed by the stress reduction process, it is possible to controlstress in the tungsten film.

<Example of Processing Apparatus Used in Stress Reduction Process>

FIG. 2 is a sectional view showing an example of a processing apparatuswhich is used in the stress reduction process. This processing apparatusis configured as a film forming apparatus which is capable of performingboth the ALD-based and the CVD-based film formation modes.

A processing apparatus 100 includes a chamber 1, a susceptor 2configured to horizontally support a semiconductor wafer (hereinafter,simply referred to as a “wafer”) W as a target substrate inside thechamber 1, a shower head 3 configured to supply a process gas into thechamber 1 in the form of a shower, an exhaust part 4 configured toexhaust an interior of the chamber 1, a process gas supply mechanism 5configured to supply the process gas into the shower head 3, and acontroller 6.

The chamber 1 is made of a metal such as Al and has a substantiallycylindrical shape. A loading/unloading port 11 through which the wafer Wis loaded into and unloaded from the chamber 1 is formed in a sidewallof the chamber 1. The loading/unloading port 11 is opened and closed bya gate valve 12. An annular exhaust duct 13 having a rectangularcross-section is installed on a main body of the chamber 1. The exhaustduct 13 has a slit 13 a formed along an inner peripheral surface of theexhaust duct 13. Further, the exhaust duct 13 has an exhaust port 13 bformed in an outer wall of the exhaust duct 13, A ceiling wall 14 isinstalled on a top face of the exhaust duct 13 so as to block an upperopening of the chamber 1. A sealing ring 15 is air-tightly installedbetween the ceiling wall 14 and the exhaust duct 13.

The susceptor 2 has a disk shape which corresponds to a size of thewafer W, and is supported by a support member 23. The susceptor 2 ismade of a ceramic material such as an aluminum nitride (AlN) or ametallic material such as an aluminum- or nickel-based alloy. A heater21 for heating the wafer W is embedded in the susceptor 2. The heater 21is configured to generate heat based on power supplied from a heaterpower supply (not shown). An output of the heater 21 is controlledaccording to a temperature signal obtained at a thermocouple (not shown)such that the wafer W is controlled to a predetermined temperature. Thethermocouple is installed near a wafer mounting surface (where the waferW is mounted) in an upper surface of the susceptor 2.

The susceptor 2 is provided with a cover member 22 made of ceramics suchas alumina to cover an outer peripheral area of the wafer mountingsurface and a lateral side of the susceptor 2.

The support member 23 configured to support the susceptor 2 isconfigured to extend from the center of a lower surface of the susceptor2 toward a position below the chamber 1 through a hole formed in abottom wall of the chamber 1. A lower end of the support member 23 isconnected to an elevating mechanism 24. With an operation of theelevating mechanism 24, the susceptor 2 is configured to vertically movebetween a process position a current position of the susceptor 2 shownin FIG. 2) and a transfer position (indicated by a dashed double-dottedline in FIG. 2) where the wafer W can be transferred, by the supportmember 23. Further, a flange part 25 through which the support member 23penetrates is installed at a position below the chamber 1. A bellows 26is installed between a bottom surface of the chamber 1 and the flange25. The bellows 26 is configured to isolate an internal atmosphere ofthe chamber 1 from ambient air and to be flexible with the verticalmovement of the susceptor 2.

Three wafer support pins 27 (only two of them are shown in FIG. 2) areinstalled to protrude upward from an elevating plate 27 a in thevicinity of the bottom surface of the chamber 1. The wafer support pins27 are configured to be lifted and lowered by the elevating plate 27 awith an operation of an elevating mechanism 28 installed below thechamber 1. Further, the wafer support pins 27 are configured topenetrate through-holes 2 a formed in the susceptor 2 placed at thetransfer position so that they come in and out of the upper surface ofthe susceptor 2. By lifting and lowering the wafer support pins 27 inthis way, the wafer W is transferred between a wafer transfer mechanism(not shown) and the susceptor 2.

The shower head 3 made of a metal is installed to face the susceptor 2,and has a diameter substantially identical to that of the susceptor 2.The shower head 3 includes a main body 31 fixed to the ceiling wall 14of the chamber 1, and a shower plate 32 connected to a lower portion ofthe main body 31. A gas diffusion space 33 is defined between the mainbody 31 and the shower plate 32. The gas diffusion space 33 is connectedto a gas inlet hole 36 which is formed to penetrate both centralportions of the main body 31 and the ceiling wall 14 of the chamber 1.The shower plate 32A has an annular protrusion 34 which is formed toprotrude downward from a peripheral portion of the shower plate 32. Gasdischarge holes 35 are formed in an inner flat surface of the showerplate 32 other than the annular protrusion 34.

When the susceptor 2 is placed at the process position, a process space37 is defined between the shower plate 32 and the susceptor 2, and theannular protrusion 34 and an upper surface of the cover member 22 of thesusceptor 2 approach each other to form an annular gap 38.

The exhaust part 4 includes an exhaust pipe 41 connected to the exhaustport 13 b of the exhaust duct 13, and an exhaust mechanism 42 connectedto the exhaust pipe 41. The exhaust mechanism 42 is provided with avacuum pump, a pressure control valve or the like. When the wafer isprocessed, a gas inside the chamber 1 flows to the exhaust duct 13through the slit 13 a, and subsequently, is exhausted from the exhaustduct 13 through the exhaust pipe 41 by the exhaust mechanism 42 of theexhaust part 4.

The process gas supply mechanism 5 includes a WCl₆ gas supply mechanism51 for supplying a WCl₆ gas used as a tungsten chloride gas that is atungsten raw material gas, a first H₂ gas supply source 52 for supplyingan H₂ gas as a main reduction gas, a second H₂ gas supply source 53 forsupplying an H₂ gas as an additive reduction gas, and a first gas supplysource 54 and a second N₂ gas supply source 55 for supplying an N₂ gasas a purge gas. Further, the process gas supply mechanism 5 includes aWCl₆ gas supply line 61 installed to extend from the WCl₆ gas supplysource 51, a first H₂ gas supply line 62 installed to extend from thefirst H₂ gas supply source 52, a second H₂ gas supply line 63 installedto extend from the second N₂ gas supply source 53, a first N₂ gas supplyline 64 which is installed to extend from the first N₂ gas supply source54 and through which the N₂ gas is supplied to the WCl₆ gas supply line61, and a second N₂ supply line 65 which is installed to extend from thesecond N₂ gas supply source 55 and through which the gas is supplied tothe first H₂ gas supply line 62.

The first N₂ gas supply line 64 is branched into a first continuous N₂gas supply line 66 through which the N₂ gas is always supplied duringthe ALD method-based film forming process, and a first flash purge line67 through which the N₂ gas is supplied only during a purge process.Similarly, the second N₂ gas supply line 65 is branched into a secondcontinuous N₂ gas supply line 68 through which the N₂ gas is alwayssupplied during the ALD method-based film forming process, and a secondflash purge line 69 through which the N₂ gas is supplied only during thepurge process. The first continuous N₂ gas supply line 66 and the firstflash purge line 67 are connected to a first connection line 70 which isconnected to the WCl₆ gas supply line 61. Further, the second H₂ gassupply line 63, the second continuous N₂ gas supply line 68 and thesecond flash purge line 69 are connected to a second connection line 71which is connected to the first H₂ gas supply line 62. The WCl₆ gassupply line 61 and the first H₂ gas supply line 62 are joined in a jointpipe 72. The joint pipe 72 is connected to the aforementioned gas inlethole 36.

At most downstream sides of the WCl₆ gas supply line 61, the first H₂gas supply line 62, the second H₂ gas supply line 63, the firstcontinuous N₂ gas supply line 66, the first flash purge line 67, thesecond continuous N₂ gas supply line 68 and the second flash purge line69, on-off valves 73, 74, 75, 76, 77, 78 and 79 for switching the supplyof respective gases during the ALD process are respectively installed.Further, mass flow controllers (MFC) 82, 83, 84, 85, 86 and 87 as flowrate controllers are installed at upstream sides of the on-off valves74, 75, 76, 77, 78 and 123 of the first H₂ gas supply line 62, thesecond H₂ gas supply line 63, the first continuous N₂ gas supply line66, the first flash purge line 67, the second continuous N₂ gas supplyline 68 and the second flash purge line 69, respectively. Furthermore,buffer tanks 80 and 81 are respectively installed in the WCl₆ gas supplyline 61 and the first H₂ gas supply line 62 such that required gases canbe supplied in a short period of time.

The WCl₆ gas supply mechanism 51 includes a film-forming raw materialtank 91 which stores WCl₆ therein. WCl₆ is solid at room temperature.Such a solid WCl₆ is stored in the film-forming raw material tank 91. Aheater 91 a is installed around the film-forming raw material tank 91 sothat the film-forming raw material within the film-forming raw materialtank 91 is heated to a suitable temperature, thus sublimating the WCl₆material The WCl₆ gas supply line 61 is inserted into the film-formingraw material tank 91 from above.

Further, the WCl₆ gas supply mechanism 51 includes: a carrier gas pipe92 inserted into the film-forming raw material tank 91 from above; acarrier N₂ gas supply source 93 for supplying an N₂ gas as a carrier gasto the carrier gas pipe 92; a mass flow controller (MFC) 94 as a flowrate controller and on-off valves 95 a and 95 b positioned at adownstream side of the mass flow controller 94, which are connected tothe carrier gas pipe 92; and on-off valves 96 a and 96 b and a flowmeter(MFM) 97, which are installed in the WCl₆ gas supply line 61 in thevicinity of the film-forming raw material tank 91. In the carrier gaspipe 92, the on-off valve 95 a is installed directly below the mass flowcontroller 94, whereas the on-off valve 95 b is installed at a sidewhere the carrier gas pipe 92 is inserted into the film-forming rawmaterial tank 91. The on-off valves 96 a and 96 b and the flowmeter 97are sequentially arranged in the WCl₆ gas supply line 61 starting from aside where the WCl₆ gas supply line 61 is inserted into the film-formingraw material tank 91.

A bypass pipe 98 is installed to connect a portion between the on-offvalve 95 a and the on-off valve 95 b in the carrier gas pipe 92 to aportion between the on-off valve 96 a and the on-off valve 96 b in theWCl₆ gas supply line 61. The bypass pipe 98 includes an on-off valve 99installed therein. By closing the on-off valves 95 b and 96 a andopening the on-off valves 99, 95 a and 96 b, the N₂ gas supplied fromthe carrier N₂ gas supply source 93 is introduced to the WCl₆ gas supplyline 61 through a series of the carrier gas pipe 92 and the bypass pipe98 so that the WCl₆ gas supply line 61 can be purged.

One end of an EVAC pipe 101 is connected to a downstream position of theflowmeter 97 in the WCl₆ gas supply line 61 and the other end thereof isconnected to the exhaust pipe 41. On-off valves 102 and 103 areinstalled in the vicinity of the WCl₆ gas supply line 61 and the exhaustpipe 41 in the EVAC pipe 101, respectively. Further, an on-off valve 104is installed at a downstream side of a connection position where theEVAC pipe 101 is connected to the WCl₆ gas supply line 61. The on-offvalves 104, 99, 95 a and 95 b are closed and the on-off valves 102, 103,96 a and 96 b are opened to vacuum-exhaust the interior of thefilm-forming raw material tank 91 by the exhaust mechanism 42.

The controller 6 includes: a process controller equipped with amicroprocessor (computer) for controlling respective components of theprocessing apparatus 100, i.e., the valves, the power supplies, theheaters, the pumps and the like; a user interface; and a storage part.The respective components of the processing apparatus 100 are configuredto be electrically connected to the process controller such that theyare controlled by the process controller. The user interface isconnected to the process controller, and includes a keyboard thatenables an operator to input commands for managing the respectivecomponents of the processing apparatus 100, a display that visuallydisplays operational states of the respective components of theprocessing apparatus 100, and the like. The storage part is alsoconnected to the process controller and stores a control program forimplementing various processes which are performed in the processingapparatus 100 under the control of the process controller; a controlprogram (i.e., a process recipe) for executing predetermined processesin the respective components of the processing apparatus 100 dependingon process conditions; various databases; or the like. The processingrecipe is stored in a storage medium (not shown) of the storage part.The storage medium may be a fixedly-installed medium such as a harddisk, or a portable medium such as a CDROM, a DVD and a semiconductormemory. Further, the process recipe may be appropriately transmittedfrom another device through, e.g., a dedicated line. If necessary, apredetermined process recipe may be called from the storage partaccording to an instruction from the user interface and then executed bythe process controller so that a desired process is performed in theprocessing apparatus 100 under the control of the process controller.

In the processing apparatus 100 configured as above, the stressreduction process is performed as follows. First, in a state where thesusceptor 2 is lowered to be positioned at the transfer position, thegate valve 12 is opened such that the wafer W having a highly-stressedtungsten film formed thereon is loaded into the chamber 1 through theloading/unloading port 11 by a transfer device (not shown).Subsequently, the wafer W is mounted on the susceptor 2 which has beenheated to a predetermined temperature by the heater 21. The susceptor 2is lifted up to the process position. The interior of the chamber 1 isvacuum-exhausted to a predetermined degree of vacuum. The on-off valves104, 95 a, 95 b and 99 are closed and the on-off valves 102, 103, 96 aand 96 b are opened so that the interior of the film-forming rawmaterial tank 91 is vacuum-exhausted through the EVAC pipe 101.Thereafter, the on-off valves 76 and 78 are opened and the on-off valves73, 74, 75, 77 and 79 are closed such that the N₂ gases supplied fromthe first N₂ gas supply source 54 and the second N₂ gas supply source 55are respectively introduced into the chamber 1 through the firstcontinuous N₂ gas supply line 66 and the second continuous N₂ gas supplyline 68, thereby increasing the internal pressure of the chamber 1 andstabilizing the temperature of the wafer W mounted on the susceptor 2.

After the internal pressure of the chamber reaches a predeterminedpressure, the on-off valves 102 and 103 are closed and the on-off valves104, 95 a and 95 b are opened such that the internal pressure of thefilm-forming raw material tank 91 is increased, thus establishing acondition in which the WCl₆ gas as the tungsten raw material can besupplied.

In this state, the WCl₆ gas as the film-forming raw material gas, the H₂gas as the reduction gas, and the N₂ gas as the purge gas are suppliedin a sequential manner as described below such that the stress reductionprocess is continuously performed.

FIG. 3 is a view showing an example of a gas supply sequence whenperforming the stress reduction process.

First, the on-off valves 76 and 78 are opened and the N₂ gases arecontinuously supplied from the first N₂ gas supply source 54 and thesecond N₂ gas supply source 55 through the first continuous N₂ gassupply line 66 and the second continuous N₂ gas supply line 68. Further,the on-off valves 73 and 75 are opened and the WCl₆ gas is supplied fromthe WCl₆ gas supply mechanism 51 through the WCl₆ gas supply line 61into the process space 37 in the chamber 1. The H₂ gas (i.e., theadditive H₂ gas) as the additive reduction gas is supplied into thechamber 1 through the second H₂ gas supply line 63 extending from thesecond H₂ gas supply source 53 (in Step S1). At this time, the WCl₆ gasis first stored in the buffer tank 80 and then supplied into the chamber1.

In Step S1, WCl₆ is adsorbed onto a surface of the wafer W. At WCl₆ isactivated by the H₂ gas which is simultaneously supplied into thechamber 1.

Subsequently, while the N₂ gas is continuously supplied through thefirst continuous N₂ gas supply line 66 and the second continuous N₂ gassupply line 68, the on-off valves 73 and 75 are closed to stop thesupply of the WCl₆ gas and the H₂ gas, and simultaneously, the on-offvalves 77 and 79 are opened to supply the N₂ gas (i.e., a flash purge N₂gas) through the first flash purge line 67 and the second flash purgeline 69. Thus, a high flow rate of the N₂ gas purges an extra WCl₆ gasand the like existing in the process space 37 (in Step S2).

Subsequently, the on-off valves 77 and 79 are closed to stop the supplyof the N₂ gas through the first flash purge line 67 and the second flashpurge line 69, while the N₂ gas is continuously supplied through thefirst continuous N₂, gas supply line 66 and the second continuous N₂ gassupply line 68. At this state, the on-off valve 74 is opened to supplythe H₂ gas (i.e., the main H₂ gas) as the main reduction gas from thefirst H₂ gas supply source 52 into the process space 37 through thefirst H₂ gas supply line 62 (in Step S3). At this time, the H₂ gas isfirst stored in the buffer tank 81 and then supplied into the chamber 1.

In Step S3, WCl₆ adsorbed onto the water W is reduced. At this time, aflow rate of the main H₂ gas corresponds to a sufficient level to inducethe reduction reaction and is lower than that of the additive H₂ gas inStep S1.

Subsequently, while the N₂ gas is continuously supplied through thefirst continuous N₂ gas supply line 66 and the second continuous N₂ gassupply line 68, the on-off valve 74 is closed to stop the supply of theH₂ gas through the first H₂ gas supply line 62, and the on-off valves 77and 79 are opened to stop the supply of the N₂ gas (i.e., the flashpurge N₂ gas) through the first flash purge line 67 and the second flashpurge line 69. Thus, like in Step S2, a high flow rate of the N₂ gaspurges the extra H₂ gas existing in the process space 37 (in Step S4).

A single cycle including Steps S1 to S4 described above is performed ina short period of time to form a unit tungsten film having a thinthickness. Further, the single cycle including Steps 1 to 4 is repeateda multiple number of times to form a process film having a desired filmthickness. The film thicknesses of the process film at this time can becontrolled according to the number of repetitions of the single cycle.

In Step S1, in parallel with the supply of the WCl₆ gas, the additivereduction gas is also supplied through the second H₂ gas supply line 63to activate the WCl₆ gas. This facilitates a film formation reaction inthe subsequent Step S3. It is therefore possible to keep the stepcoverage at a high level and increase a thickness of the film formed percycle, thus increasing a film forming rate. The flow rate of the H₂ gasat this time needs to be controlled to suppress the CVD-based reactionwhile ensuring the ALD-based reaction. Thus, the flow rate of the H₂ gasmay range from 100 to 500 sccm (mL/min). In some embodiments, as shownin FIG. 4, the additive H₂ gas may be always supplied through the secondH₂ gas supply line 63 during the period of Steps S2 to S4. With thisconfiguration, when the WCl₆ gas is supplied, the additive H₂ gas as theadditive reduction gas is also supplied, thus activating the WCl₆ gas.The flow rate of the H₂ gas at this time may range from 10 to 500 sccm(mL/min) from the viewpoint of suppressing the CVD-based reaction andkeeping the ALD-based reaction. However, if a good film formationreaction is induced even in the absence of the additive H₂ gas, theadditive H₂ gas may be omitted.

In the above sequence, the N₂ gas as the purge gas always flows from thefirst continuous N₂ gas supply line 66 and the second continuous N₂ gassupply line 68 to the WCl₆ gas supply line 61 and the first H₂ gassupply line 62 during the period of Steps S1 to S4, while the WCl₆ gasand the H₂ gas are intermittently supplied in Steps S1 and S3. It istherefore possible to improve a replacement efficiency of gas inside theprocess space 37. Further, the N₂ gas is supplied through each of thefirst flash purge line 67 and the second flash purge line 69 to purgethe process space 37 in Steps S2 and S4. This further improves thereplacement efficiency of gas inside the process space 37. It istherefore possible to control the thickness of the tungsten film at agood level.

In the processing apparatus 100 shown in FIG. 2, the buffer tanks 80 and81 are installed in the WCl₆ gas supply line 61 and the first H₂ gassupply line 62, respectively. This facilitates the supply of the WCl₆gas and the H₂ gas in a short period of time. Thus, even if a period ofthe single cycle is short, it is possible to easily supply the WCl₆ gasand the gas at a flow rate required for Steps S1 and S3.

In some embodiments, when the stress reduction process is performed bythe CVD method, the WCl₆ gas and H₂ gas are simultaneously suppliedthrough the WCl₆ gas supply line 61 and the first H₂ gas supply line 62,respectively.

<Process Conditions>

The following is an example of process conditions of the stressreduction process.

i) ALD

Pressure: 5 to 50 Torr (666.5 to 6,665 Pa)

Temperature: 300 degrees C. or more some embodiments, 450 to 600 degreesC.)

Flow Rate of WCl₆ Gas: 3 to 60 sccm (mL/min)

-   -   (Flow Rate of Carrier Gas: 100 to 2,000 sccm (mL/min))

Partial Pressure of WCl₆ Gas: 0.5 to 10 Torr (66.7 Pa to 1,333 Pa)

Flow Rate of Main H₂ Gas: 2,000 to 8,000 sccm (mL/min)

Flow Rate of Additive H₂ Gas: 100 to 500 sccm (mL/min)

Flow Rate of Continuously-Supplied N₂ Gas: 100 to 500 sccm (mL/min)

-   -   (through the first and second continuous N₂ gas supply lines 66        and 68)

Flow Rate of Flash Purge N₂ Gas: 500 to 3000 sccm (mL/min)

-   -   (through the first and second flash purge lines 67 and 69)

Period of Time of Step S1 (Per cycle): 0.01 to 5 sec

Period of Time of Step S3 (Per cycle): 0.1 to 5 sec

Period of Times of Steps S2 and S4 (Purging) (Per cycle): 0.1 to 5 sec

Period of Supply Time of Additive H₂ Gas in Step S1 (Per cycle): 0.01 to0.3 sec

Heated Temperature of Film-forming Raw Material Tank: 130 to 190 degreesC.

ii) CVD

Pressure: 5 to 50 Torr (666.5 to 6,665 Pa)

Temperature: 300 degrees C. or more (In some embodiments, 450 to 600degrees C.)

Flow Rate of WCl₆ Gas: 3 to 60 sccm (mL/min)

-   -   (Flow Rate of Carrier Gas: 100 to 2,000 sccm (mL/min))

Partial Pressure of WCl₆ Gas: 0.5 to 10 Torr (66.7 Pa to 1,333 Pa)

Flow Rate of Main H₂ Gas: 2,000 to 8,000 sccm (mL/min)

Flow Rate of N₂ Gas: 100 to 500 sccm (mL/min)

<First Embodiment of Film Forming Method>

Next, a first embodiment of a method of forming a tungsten film will bedescribed.

This example is an example in which a tungsten film is formed using theWCl₆ gas and the H₂ gas and subsequently, the stress reduction processis performed.

In the first embodiment, for example, as shown in FIG. 5, a firsttungsten film 303 is formed on a wafer W having an insulation film 301(such as an SiO₂ film) followed by a base film 302 by the ALD methodusing the WCl₆ gas and the H₂ gas. Although in FIG. 5 the insulationfilm 301 and the base film 302 has been shown in a planar shape for thesake of simplicity, fine complex-shaped concave portions are formed inthe insulation film 301 in practice, and the base film 302 is formed onthe insulation film 301 along such concave portions.

An example of the base film 302 may include a titanium-based materialfilm such as a TiN film, a TiSiN film, a Ti silicide film, a Ti film, aTiON film, a TiAlN film or the like. In some embodiments, an example ofthe base film 302 may include a tungsten-based compound film such as aWN film, a WSi_(x) film, a WSiN film or the like. The formation of thebase film 302 on the insulation film 301 allows the tungsten film to beformed with good adhesion.

When the TiN film is used as the base film 302, the WCl₆ gas as thetungsten chloride gas and the H₂ gas as the reduction gas aresequentially supplied into the chamber 1 while purging the interior ofthe chamber 1 in the course of sequentially supplying the gases, suchthat the first tungsten film 303 is formed on the base film 302 by theALD method. In this case, as shown in FIG. 6, in a region where thefirst tungsten film 303 is hardly deposited or a deposition amountthereof is small, the WCl₆ gas is directly supplied to the TiN film sothat an etching reaction between the TiN film and the WCl₆ gas occurs asfollows:TiN(s)+WCl₆(g)→TiCl₄(g)+WCl_(x)(g)  (3)

Similarly, even when other titanium-based material films andtungsten-based compound films are used as the base film 302, the basefilm 302 is etched by the WCl₆ gas as the tungsten chloride gas.

In order to suppress the etching of the base film 302, the WCl₆ gas issupplied at a relatively low flow rate such that the first tungsten film303 is formed. As described above, since the first tungsten film 303 isformed by the WCl₆ gas of the relatively low flow rate, a small amountof HCl gas is generated, thus suppressing the first tungsten film 303from being etched by the generated HCl gas. This causes distortionbetween tungsten crystal grains so that the first tungsten film 303 ishighly-stressed.

At this time, the first tungsten film 303 can be formed using a filmforming apparatus having the same structure as that of the processingapparatus 100 of FIG. 2. A film formation process performed at this timeis the ALD method.

An example of film formation conditions of the highly-stressed firsttungsten film 303 is as follows:

Pressure: 20 to 100 Torr (2,666 to 13,330 Pa)

Temperature: 300 degrees C. or more (in some embodiments, 450 to 600degrees C.)

Flow Rate of WCl₆ Gas: 0.1 to 10 sccm (mL/min)

-   -   (Flow Rate of Carrier Gas: 1 to 1,000 sccm (mL/min))

Partial Pressure of WCl₆ Gas (previously described): 1 Torr (133.3 Pa)or less (in some embodiments, 0.1 Torr (13.33 Pa) or less)

Flow Rate of Main H₂ Gas: 10 to 5,000 sccm (mL/min)

Flow Rate of Continuously-Supplied N₂ Gas: 10 to 10,000 sccm (mL/min)

-   -   (through the first and second continuous N₂ gas supply lines 66        and 68)

Flow Rate of Flash Purge N₂ Gas: 100 to 100,000 sccm (mL/min)

-   -   (through the first and second flash purge lines 67 and 69)

Period of Time of Step S1 (Per Cycle): 0.01 to 5 sec

Period of Time of Step S3 (Per Cycle): 0.1 to 5 sec

Period of Time of each of Steps S2 and S4 (Purging) (Per Cycle): 0.1 to5 sec

Period of Supply Time of Additive H₂ Gas in Step S1 (Per Cycle): 0.01 to0.3 sec

Heated Temperature of Film-forming Raw Material Tank: 130 to 190 degreesC.

An example of the tungsten chloride used when forming the first tungstenfilm 303 may include WCl₅ and WCl₄ in addition to the aforementionedWCl₆. Among these materials, WCl₆ may be preferably used.

Further, the reduction gas is not limited to the H₂ gas but may be otherreduction gases which contain hydrogen. Instead of the H₂ gas, an SiH₄gas, a B₂H₆ gas, an NH₃ gas or the like may be used as the reductiongas. Alternatively, two or more of the H₂ gas, the SiH₄ gas, the B₂H₆gas and the NH₃ gas may be supplied. Moreover, in addition to thesegases, other reduction gases such as a PH₃ gas or an SiH₂Cl₆ gas may beused. From the viewpoint of further decreasing impurities in the film toobtain a low resistance value, the H₂ gas may be used.

After the first tungsten film 303 is formed in the above way, the stressreduction process as described above is performed to form a secondtungsten film 304 as a process film on the first tungsten film 303.Thus, a tungsten film 305 that is lowly stressed is formed. Further, thesecond tungsten film 304 as the process film is formed in the samemanner as the process film 204 described above.

Film thicknesses of the first tungsten film 303 and the second tungstenfilm 304 may be appropriately determined. Since the first tungsten film303 that is highly-stressed is formed from the viewpoint of suppressingthe etching of the base film 302, the first tungsten film 303 may beformed to have a thin thickness of 10 nm or less. Meanwhile, since thesecond tungsten film 304 is formed to reduce the stress in the firsttungsten film 303, the second tungsten film 304 may be formed to have athickness that is thin enough to obtain the stress reduction effect.However, since the second tungsten film 304 constitutes a portion of thetungsten film 305, the second tungsten film 304 may be formed to have athickness that is thick enough to satisfy a desired thickness of thetungsten film 305.

The process of initially forming the first tungsten film 303 and thesubsequent stress reduction process may be performed in-situ using asingle apparatus without being exposed to the atmosphere. In someembodiments, the initial process of forming the first tungsten film 303is performed and subsequently, the formed first tungsten film 303 may beexposed to the atmosphere and may be subjected to the stress reductionprocess in a separated apparatus ex-situ. From the viewpoint ofimproving the stress reduction effect as will be described below, thein-situ process may be applied.

Actually, the present inventors performed an experiment to measure filmstresses applied to the first tungsten film 303, the second tungstenfilm 304, and the tungsten film 305 including the first tungsten film303 and the second tungsten film 304, when forming the first tungstenfilm 303 in a thickness of about 15 nm through the use of the ALD methodusing the WCl₆ gas and the H₂ gas under a condition that a film stressis increased, following by performing the stress reduction processin-situ using the same apparatus to form the second tungsten film 304having a thickness of about 15 nm as the process film. The results ofthe experiment are shown in FIG. 8. As shown in FIG. 8, the firsttungsten film 303 was highly-stressed at a level of 2015 MPa, whereasthe second tungsten film 304 formed by the stress reduction process wasslightly stressed at a level of −4.8 MPa. Meanwhile, the tungsten film305 including the first tungsten film 303 and the second tungsten film304 was stressed at a level of 148.5 Pa. Accordingly, the experimentshows that the film stress was significantly reduced by the stressreduction process.

Further, examination has been performed to confirm a relationshipbetween the number of cycles of the stress reduction process and a filmstress in the tungsten film obtained by the stress reduction process.FIG. 9 is a view showing a film stress applied to the tungsten film 305including the first tungsten film 303 and the second tungsten film 304,when forming the first tungsten film 303 by the ALD method using theWCl₆ gas and the H₂ gas under a condition that a film stress isincreased, following by performing the stress reduction process in-situusing the same apparatus while varying the number of cycles by the ALDmethod. In FIG. 9, 300 cycles correspond to an example of where a filmthickness of the second tungsten film 304 becomes 2.5 nm. As shown inFIG. 9, it is confirmed that, even if the second tungsten film 304 asthe process film is thin at the level of 2.5 nm, a sufficient stressreduction effect is obtained.

Then, the present inventors confirmed a stress reduction effect when thestress reduction process was performed in-situ and ex-situ while varyingthe film thickness of the highly-stressed tungsten film 303. The resultsare show in FIG. 10. As shown in FIG. 10, it can be seen that thethinner the highly-stressed first tungsten film 303, the higher theeffect of the stress reduction process is. Moreover, it can be seen thatperforming the stress reduction process in-situ has a higher stressreduction effect than performing the stress reduction process ex-situ.

The reason why the effect of the ex-situ process is low is that if thewafer is exposed to the atmosphere after the formation of thehighly-stressed first tungsten film 303, air may enter to spaces definedbetween tungsten crystal grains, which impedes the subsequent stressreduction process. For this reason, the stress reduction process isperformed in-situ rather than ex-situ. In a case where the stressreduction process is required to be performed ex-situ, a sequence offorming the first tungsten film 303 and discharging air existing betweencrystal grains may be effective.

<Second Embodiment of Film Forming Method>

Next, a second embodiment of a film forming method will be described.

In this example, a tungsten film is formed using the WF₆ gas and the H₂gas and subsequently, the stress reduction process using a WCl₆ gas andthe H₂ gas is performed to form a film.

When the tungsten film is formed by the CVD method using the WF₆ gas,fluorine contained in WF₆ reduces agate insulation film, whichdeteriorates an electric property. As such, the use of a WCl₆ gas isunder consideration instead of the WF₆ gas. However, since WF₆ is muchcheaper than WCl₆, WF₆ is being used with research of a barrier film.

In this example, the formation of the tungsten film is formed asfollows. For example, as shown in FIG. 11, a first tungsten film 403 isformed on a wafer W in which a base film 402 is formed on an insulationfilm 401 such as an SiO₂ film, using the WF₆ gas and the gas. Althoughin FIG. 11, the insulation film 401 and the base film 402 are shown inplanar shapes for the sake of simplicity, the insulation film 401 may beformed with fine complex-shaped concave portions in practice, and thebase film 402 may be formed along the concave portions.

An example of the base film 402 may include a titanium-based materialfilm such as a TiN film, a TiSiN film, a Ti silicide film, a Ti film, aTiON film, a TiAlN film or the like. In some embodiments, an example ofthe base film 402 may include a tungsten-based compound film such as aWN film, a WSi_(x) film, a WSiN film or the like. The formation of thebase film 402 allows the tungsten film to be formed with good adhesion.

The tungsten film formed using the WCl₆ gas and the H₂ gas is known tobe highly-stressed. Even in this case, it is considered that stress insuch a tungsten film is caused due to distortion between tungstencrystal grains. As such, the first tungsten film 403 is also stressed ata high level of e.g., 1,000 MPa or more.

Thus, as shown in FIG. 12, after the first tungsten film 403 is formed,a second tungsten film 404 as a process film is formed by theaforementioned stress reduction process using the WCl₆ gas and the H₂gas. As a result, a tungsten film 405 that is lowly stressed is formed.Further, the second tungsten film 404 as the process film is formed inthe same manner as the process film 304 described above.

At this time, thicknesses of the first tungsten film 403 and the secondtungsten film 404 may be appropriately set. From the viewpoint ofcost-saving, the first tungsten film 403 using the WF₆ gas may be formedas thick as possible. In this case, the second tungsten film 404 may beformed to have a thickness thin enough to obtain the stress reductioneffect.

Further, the reduction gas is not limited to the H₂ gas but may be otherreduction gases which contain hydrogen. Instead of the H₂ gas, an SiH₄gas, a B₂H₆ gas, an NH₃ gas or the like may be used as the reductiongas. Alternatively, two or more of the H₂ gas, the SiH₄ gas, the B₂H₆gas and the NH₃ gas may be supplied. Moreover, in addition to thesegases, other reduction gases such as a PH₃ gas or an SiH₂Cl₆ gas may beused. From the viewpoint of further decreasing impurities in the film toobtain a low resistance value, the H₂ gas may be used.

The first tungsten film 403 may be formed by the ALD or CVD methodusing, e.g., the conventional film forming apparatus.

Specifically, a primary step of supplying the WF₆ gas, and the H₂ gas,the SiH₄ gas, the B₂H₆ gas or the like as the reduction gas at low flowrates to form the first tungsten film 403 by the ALD method and asecondary step of supplying the WF₆ gas and the H₂ gas as the reductiongas at high flow rates to form a main tungsten film, are performed suchthat a nucleation tungsten film is formed. In some embodiments, the SiH₄gas or the B₂H₆ gas having a high reduction capacity may be used as thereduction gas used when forming the nucleation tungsten film. In someembodiments, an example of a film formation temperature may fall withina range of approximately 300 to 500 degrees C.

Further, in a case where the first tungsten film 403 and the secondtungsten film 404 are formed in-situ, since WF₆ is in a gaseous state atroom temperature, as shown in FIG. 13, a processing apparatus 100′ whichfurther includes a WF₆ gas supply source 120 in addition to theprocessing apparatus 100 shown in FIG. 2 may be used to switch thesupply of the WCl₆ gas and the WF₆ gas. The WF₆ gas supply source 120 isconnected to a WF₆ gas supply line 121 which is joined with the WCl₆ gassupply line 61 at an upstream side of the connection position betweenthe WCl₆ gas supply line 61 and the EVAC pipe 101. A mass flowcontroller 122 as a flow rate controller and an on-off valve 123 areinstalled in the WF₆ gas supply line 121. Further, an on-off valve 124is installed in the WCl₆ gas supply line 61 at an upstream side of wherethe WCl₆ gas supply line 61 and the WF₆ gas supply line 121 are joined.

With the processing apparatus 100′, the first tungsten film 403 isformed using the WF₆ gas and subsequently, the second tungsten film 404is formed using the WCl₆ gas in-situ, which makes it possible to improvea stress reduction effect.

<Other Applications>

While the present disclosure has described exemplary embodiments, thepresent disclosure is not limited thereto, but may be modified in avariety of forms. As an example, although in the above embodiments, thetungsten chloride gas and the reduction gas has been described to beused for the stress reduction process of the tungsten film, the presentdisclosure is not limited thereto. In some embodiments, a chloride gasof another metal film and a reduction gas may be used to reduce stressin the respective metal film. As an example, the present disclosure maybe applied to a case where a molybdenum chloride gas and a reduction gasare used to reduce stress in a molybdenum film or a case where atantalum chloride gas and a reduction gas are used to reduce stress in atantalum film.

Further, although in the above embodiments, the semiconductor wafer hasbeen described to be used as a target substrate, the semiconductor wafermay be a silicon substrate, or a compound semiconductor such as GaAs,SiC and GaN or the like. The present disclosure is not limited to thesemiconductor wafer but may be also applied to a glass substrate used ina flat panel display (FPD) such as a liquid crystal display, a ceramicsubstrate or the like.

According to the present disclosure in some embodiments, ahighly-stressed metal film is processed by a metal chloride gascontaining a respective metal and a reduction gas for reducing the metalchloride gas which are supplied thereonto, so that a process film isformed on the metal film. Thus, it is possible to reduce stress in thehighly-stressed metal film.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the embodiments described herein may beembodied in a variety of other forms. Furthermore, various omissions,substitutions and changes in the form of the embodiments describedherein may be made without departing from the spirit of the disclosure.The accompanying claims and their equivalents are intended to cover suchforms or modifications as would fall within the scope and spirit of thedisclosure.

What is claimed is:
 1. A method of reducing stress in a metal film thatis highly stressed, the method comprising: processing the metal film toreduce stress in the metal film by supplying a metal chloride gascontaining a metal of the metal film and a reduction gas for reducingthe metal chloride gas onto the metal film so as to perform: etching themetal film by HCl generated from a reaction between the metal chloridegas and the reduction gas to generate gaps between crystal grains of themetal film; and forming a process film in the gaps and on a surface ofthe metal film.
 2. The method of claim 1, wherein the processing themetal film is performed by loading a target substrate having the metalfilm formed thereon into a chamber maintained under a depressurizedatmosphere; and sequentially or simultaneously supplying the metalchloride gas and the reduction gas into the chamber such that theprocess film is formed on the metal film.
 3. The method of claim 1,wherein the stress in the metal film is controlled by adjusting aprocess condition and a thickness of the process film in the processingthe metal film.
 4. The method of claim 1, wherein the metal film is atungsten film, and the metal chloride gas used in the processing themetal film is a tungsten chloride gas.
 5. The method of claim 4, whereinthe processing the metal film is performed under a condition that apartial pressure of the tungsten chloride gas ranges from 0.5 to 10Torr.
 6. The method of claim 4, wherein the tungsten film as the metalfilm is formed by loading the target substrate into the chambermaintained under the depressurized atmosphere and sequentially supplyingthe tungsten chloride gas and the reduction gas into the chamber,wherein a flow rate of the tungsten chloride gas when forming the metalfilm is lower than that of the tungsten chloride gas in the processingthe metal film.
 7. The method of claim 6, wherein a partial pressure ofthe tungsten chloride gas when forming the tungsten film as the metalfilm is 1 Torr or less.
 8. The method of claim 4, wherein the tungstenfilm as the metal film is formed by loading the target substrate intothe chamber maintained under the depressurized atmosphere and supplyinga WF₆ gas and the reduction gas into the chamber.
 9. The method of claim4, wherein the tungsten chloride is one of WCl₆, WCl₅, and WCl₄.
 10. Themethod of claim 1, wherein the reduction gas is at least one of an H₂gas, an SiH₄ gas, a B₂H₆ gas and an NH₃ gas.
 11. The method of claim 1,wherein the stress in the metal film before processing the metal film is1,000 MPa or more.
 12. A method of forming a metal film, comprising:forming a metal film on a target substrate; and processing the metalfilm to reduce stress in the metal film by supplying a metal chloridegas containing a metal of the metal film and a reduction gas forreducing the metal chloride gas so as to perform: etching the metal filmby HCl generated from a reaction between the metal chloride gas and thereduction gas to generate gaps between crystal grains of the metal film;and forming a process film in the gaps and on a surface of the metalfilm.
 13. The method of claim 12, wherein the process film is formed byloading the target substrate with the metal film formed thereon into achamber maintained under a depressurized atmosphere and sequentially orsimultaneously supplying the metal chloride gas and the reduction gasinto the chamber.
 14. The method of claim 12, wherein the stress in themetal film is controlled by adjusting a process condition and athickness of the process film in the forming a process film.
 15. Themethod of claim 12, wherein the stress in the metal film beforeprocessing the metal film is 1,000 MPa or more.
 16. A method of forminga metal film, comprising: forming a first tungsten film as the metalfilm by sequentially supplying a tungsten chloride gas and a reductiongas for reducing the tungsten chloride gas onto a target substrate; andforming a second tungsten film as a process film on the first tungstenfilm by performing a process on the target substrate to reduce stress inthe first tungsten film, the process including sequentially orsimultaneously supplying the tungsten chloride gas and the reduction gasfor reducing the tungsten chloride gas onto the target substrate withthe first tungsten film formed thereon so as to perform: etching themetal film by HCl generated from a reaction between the metal chloridegas and the reduction gas to generate gaps between crystal grains of thefirst tungsten film; and forming the second tungsten film in the gapsand on a surface of the first tungsten film, wherein a flow rate of thetungsten chloride gas in the forming a first tungsten film is lower thanthat of the tungsten chloride gas in the forming the second tungstenfilm.
 17. The method of claim 16, wherein a partial pressure of thetungsten chloride gas in the forming a first tungsten film is 1 Torr orless, and a partial pressure of the tungsten chloride gas in the forminga second tungsten film ranges from 0.5 to 10 Torr.
 18. The method ofclaim 16, wherein, in the forming a first tungsten film and the forminga second tungsten film, a temperature of the target substrate is 300degrees C. or more and a pressure is 5 Torr or more.
 19. The method ofclaim 16, wherein the tungsten chloride is one of WCl₆, WCl₅, and WCl₄.20. The method of claim 16, wherein the reduction gas is at least one ofan H₂ gas, an SiH₄ gas, a B₂H₆ gas and an NH₃ gas.
 21. The method ofclaim 16, wherein the stress in the first tungsten film is 1,000 MPa ormore.